(1) Field of the Invention
The present invention relates to a solid-state imaging device utilized in digital cameras and the like, and particularly to a solid-state imaging device with a function for correcting a field curvature caused by aberration of an optical imaging system.
(2) Description of the Related Art
Together with the rapid spread of digital still cameras, cell phone cameras and the like, the market for solid-state imaging devices has significantly developed. In addition, along with an increasing demand for thinner digital still cameras and cell phone cameras, miniaturization of camera modules has become a major concern. Miniaturization of the camera modules requires reduction of the number of lenses for an optical system, and thus the focal length of the optical system becomes short. As a result, the reduction of the number of lenses makes it difficult to correct a field curvature caused by an aberration and incident light on a solid-state imaging device has a wide incident angle at the periphery (a wide angle against a vertical axis of an incidence plane of a solid-state imaging device).
On this account, a solid-state imaging apparatus or the like which corrects a field curvature caused by the aberration of an optical imaging system has been proposed (see Japanese Laid-Open Patent Application No. 2003-188366 (Patent Reference 1) and Japanese Translation of PCT International Application laid open as JP2004-526300 (Patent Reference 2)).
The solid-state imaging apparatus according to Patent Reference 1 is configured of thin-filmed solid-state imaging devices which are curved so as to fit a field curvature caused by an aberration of the optical imaging system. With this configuration, even if there is a field curvature caused by an aberration of an optical imaging system, imaging at a high resolution can be performed. In addition, with this configuration, since solid-state imaging devices are curved, an incident angle of light that enters in a solid-state imaging device is compensated.
In addition, in the optical imaging system according to Patent Reference 2, a step is installed for a curved surface corresponding to a field curvature which occurs due to the aberration of the optical imaging system, and microlenses of different focal lengths are set adaptively. With this configuration, it is possible to correct field curvatures. In addition, there is a disclosure of a technology regarding correction of a field curvature. According to this technology, diameter of microlens increases toward the periphery of a solid-state imaging device so as to change the focal length. In this case, light with a wide incident angle can be received relatively well since the diameter of the microlens is wider at the periphery of the solid-state imaging device.
However, with the technology disclosed in aforementioned Patent Reference 1, in the case where solid-state imaging devices are made of thin films or when devices are curved, there is a problem that a pixel defect such as white defect and the like occur due to stress caused by the curve. Furthermore, it is difficult to curve and fix the solid-state imaging devices to correct a field curvature.
In addition, with the manufacturing method for microlenses according to Patent Reference 2, it is difficult to make microlenses of different focal lengths. Note that in Patent Reference 2, the diameter of microlenses set for a solid-state imaging device increases toward the periphery of the solid-state imaging device. However, with this conventional manufacturing method for microlenses, it is difficult to manufacture microlenses of different diameters and of different focal lengths.